The advantage of metal/oxygen batteries compared with conventional batteries, is that a comparatively high energy density can be obtained, which is of great importance, e.g. if the battery is to be used for driving a vehicle. It has thus been found possible to obtain values of over 100 Wh/kg, which can be compared with about 60 Wh/kg for alkaline nickel oxide/iron batteries and about 40 Wh/kg for lead batteries.
A great drawback of the metal/oxygen cells manufactured up to now, is that an extensive auxiliary system is required to obtain a well-functioning cell. It has thus been found necessary to circulate the electrolyte, to pump oxygen or air past the gas sides of the oxygen electrodes, and to introduce a special charging electrode or other means for charging the metal electrode without destroying the oxygen electrode.
A summary of the systems which have been developed, or are under development, has been presented in "Journal of Power Sources" 2 (1977/78) pp. 287-296.
An oxygen electrode is disclosed in Swedish lay-open print No. 391,609, which is characterized in that water diffuses from the gas side towards the electrolyte during the charging phase. This is achieved by the construction of a dual layer electrode, where the layer on the gas side contains a hydrophobic material, preferably of polytetrafluoroethylene, and a catalyst for oxygen dissolution, while the layer towards the electrolyte side is hydrophilic. When built up into cells, the air electrodes are fixed into frames, and for constructing a battery, two adjacent cells form an air chamber for supplying the air electrodes with oxygen from the air.
In German Offenlegungsschrift No. 2,129,045 another metal/air or metal/oxygen battery is disclosed. In that battery a biporous oxygen (or air) electrode is used, which is layered with finely porous separators and metal electrodes to form an electrode package, where the gas electrodes are connected to a gas conduit at one or more places along the edges thereof.
The above-mentioned systems, however, have gas electrodes assembled into a pocket which is provided with gas conduits for supplying the pocket with oxygen or air from outside the pocket.
Another type of gas diffusion electrode is described in the article "Nouveau type d'electrode pour piles a combustible" published in "Advanced Energy Conversion", Vol. 7, pp. 159-166, Pergamon Press, 1967. The electrode is built up from finely-divided activated carbon bound together with the aid of a hydrophobic binder to a cohesive body with pores alternatingly filled with gas and with electrolyte. The gas is supplied from the surroundings by means of special gas supply means which can be applied anywhere on the electrode and which are described in more detail in French Pat. No. 1,433,558. Also in this case, however, there is the requirement that gas conduits, and thus special means, are applied on to the electrode for the supply of air or oxygen from outside.